Support parsing IPv6 addresses with embedded IPv4 addresses
Support parsing IPv6 addresses with embedded IPv4 addresses

IPv6 parsing now supports embedded IPv4 addresses as outlined in
RFC 4291 section 2.2. An IPv4 address following *any* 96-bit IPv6
prefix is supported.

IPv6 address formatting doesn't change and therefore doesn't ever
output IPv6 strings with embedded IPv4 addresses.

HowNetWorks/ipv46,HowNetWorks/ipv46